Stator End Region Research Articles

Influence of Temperature Rise in Stator End Region on Reactive Power Consumption Ability of Dual-Excited Synchronous Condenser

Influence of Temperature Rise in Stator End Region on Reactive Power Consumption Ability of Dual-Excited Synchronous Condenser

Fracture failure analysis of insulation with initial crack defect for stator end-winding in induction motor by using magnetic-structural coupling model

The insulation mechanic failure in stator end-winding of induction motor is usually an early and serious cause to weaken the residual breakdown electrical field strength and produce the short-circuit fault, especially subjecting to the combination of dynamical electromagnetic forces, mechanical stress and vibration. In this paper, the fracturebehavior of insulation layer with considering the initial crack defects and end-hoop support failures in end-windings were analyzed by using magnetic-structural coupling model and finite element method (FEM). Firstly, the distributions of magnetic flux density and electromagnetic force around the stator end region were determined by injecting three-phase alternating current. Secondly, the dynamic characteristics of deformation, stress and strain in winding insulation were respectively calculated by coupling the transient electromagnetic and structural analysis. Furthermore, the weak points of the concentrated stress and strain were located. Thirdly, the crack model mounted in winding insulation is defined and simulated by employing three-dimensional (3-D) semi-elliptical crack element. To evaluate the fracture mechanism and the degree of crack expansion quantitatively, the stress intensity factor (SIF) was introduced. Finally, the influence of crack location, direction, depth and end-hoop support failure on SIF and crack propagation were investigated. Results show that the concentrated stress at knuckle part of the coil insulation is lager quite larger than that of other parts. The SIF of transverse crack is larger than that of longitudinal cracks. The larger the initial crack depth in the stator end-winding insulation, the more serious the tendency and degree of crack fracture. Local end-hoop support failure also has an important influence on the crack propagation. Results in this study may contribute to the understanding of fracturefailure behaviors in insulation under dynamical electromagnetic vibration and provide necessary theoretical reference for fault diagnosis and prediction of stator winding in induction motors.

Loss Distribution in Stator End Region of Turbo-Generator during Asynchronous Operation after Different Excitation Faults

A turbo-generator during asynchronous operation after the excitation fault can absorb lots of reactive power and result in the increase of the leakage flux and losses in the stator end region. In order to study the loss distribution of the stator end structural components during asynchronous operation, this paper presents a method combining the 2-D field-circuit coupled time-stepping finite element model (FCCTSFEM) with the 3-D transient electromagnetic field in the end region of the turbo-generator. The asynchronous processes of the turbo-generator under the open- and short-circuit faults of field winding are calculated by FCCTSFEM, and 3-D transient electromagnetic field and the losses in the stator end region of the turbo-generator are calculated. From the detailed performance evaluations by the 3-D finite-element analysis, the flux densities and loss distributions of the stator end structural components are compared under different excitation faults. The influence of the metal shield material on the flux densities and losses of the stator end region is studied. The variations of the losses in different stator end structural components are revealed along with the conductivity of the metal shield. The results could provide a theoretical basis for improving the asynchronous operating ability of the turbo-generator after the excitation fault.

Dynamic response of large turbogenerator stator end winding under fault conditions

The electromagnetic fields of a 600MW turbogenerator stator end region under three-phase short circuit and two-phase short circuit are calculated by numerical simulation base on a three-dimensional electromagnetic model. The variation of electromagnetic force density can also be obtained in the same time. Then the dynamic responses consist of deformation and stress distributions of end winding under three-phase short circuit are numerically analyzed by the fine finite element model which is set up in ABAQUS software. The presented numerical models and method can in turn be used to study the dynamic responses and safety of the end structure under various operation conditions.

Large-Scale 3D Electromagnetic Field Analysis for Estimation of Stator End Region Loss in Turbine Generators

In indirectly hydrogen cooled turbine generators used in high-efficiency combined cycle power plants, improving the energy efficiency and increasing the power density are required for one of the solutions of the global environmental problems. When the output current is increased for achieving the high power density, the stray load loss at the stator end region is increased by the leakage flux from the armature and field coils. Therefore, in the case that the stray load loss at the stator end region is increased when the output capacity is increased, it is necessary to evaluate the temperature under the condition of the leading power factor load. In this paper, we analyzed the loss density distribution at the end region structures using the large-scale 3D electromagnetic field analysis to establish the temperature reliability in the 870MVA indirectly hydrogen cooled machine, which is the largest class capacity in the world. Using the loss density distribution obtained by the analysis, the thermal analysis is then performed. The analysis results show good agreements with the measured values.

Influence of Edge Permanent-Magnet Shape on the Performance of an Arc-Linear Permanent-Magnet Synchronous Machine

A kind of arc-linear permanent-magnet synchronous machine (AL-PMSM) used for scanning system, which requires high positioning accuracy, high response performance, and wide scanning range, is proposed and researched. Due to the finite length of stator core and rotor core, the AL-PMSM suffers from stator end effect and rotor end effect. The cogging torque caused by stator end effect can be reduced significantly by stator length optimization, PM shape optimization, and so on. The cogging torque caused by rotor end effect is mainly analyzed and reduced in this paper. The rotor end effect occurs when the rotor end region is close to the stator end region and the influence of rotor end effect is mainly two pole pitches. In order to reduce the cogging torque caused by rotor end effect, shape optimization of the edge permanent magnets, especially the first edge PM and second edge PM, is researched and compared. After optimization, the smooth scanning range is improved from ±47.8° to ±56.2° by 17.6% with the peak-to-peak value of cogging torque less than 0.19 Nm. The effectiveness of the optimization method is verified by the finite-element method.

Finite-Element Evaluation and Eddy-Current Loss Decrease in Stator End Metallic Parts of a Large Double-Canned Induction Motor

Large double-canned induction motor has high power density and usually works in a closed environment. Compared with a common induction motor, there are many contacted metallic parts in the stator end region of a large double-canned induction motor, in which eddy current will exist not only in end metallic parts themselves but also between contacted metallic parts. Evaluation of eddy-current losses in stator end metallic parts and reasonable end structure design is the premise of ensuring the safe and stable operation of a large double-canned induction motor. A 5-MW-scale double-canned induction motor is taken as an example in this paper, and the 3-D eddy-current field finite-element calculation model of its stator end is established and solved. Then, the eddy current in stator end metallic parts and between different contacted stator end metallic parts is analyzed in detail. On this basis, the eddy-current losses' decrease method through cutting off the eddy-current path between contacted stator end metallic parts is proposed and validated by experimental results of temperature.

3D loss and heat analysis at the end region of 4-poles 1150 MW nuclear power turbine generator

Abstract To study the principle of loss and heat at the end region of large 4-poles nuclear power turbine generator, 3D transient electromagnetic field and 3D steady temperature field finite element (FE) models of the end region are established respectively. Considering the factors such as rotor motion, core non-linearity and time-varying of electromagnetic field, the anisotropic heat conductivity and different heat dissipation conditions of stator end region, a 50 Hz, 1150 MW, 4-poles nuclear power turbine generator is investigated. The loss and heat at the generator end region are calculated respectively at no-load and rated-load, and the calculation results are compared with the test data. The result shows that the calculation model is accurate and the generator design is suitable. The method is valuable for the research of loss and heat at the end region of large 4-poles nuclear power turbine generator and the improvement of the generator’s operation stability. The method has been applied successfully for the design of the larger nuclear power turbine generators

3D Magnetic Field and Loss Analysis at the No Load Condition in the End Region of 4-Poles Large Turbine Generator

To study the principle of magnetic field and loss at the end region of large 4-poles large turbine generator, 3D transient electromagnetic field finite element (FE) models of the end region are established respectively. Considering the factors such as rotor motion, core non-linearity and time-varying of electromagnetic field, the anisotropic heat conductivity and different heat dissipation conditions of stator end region, a 50Hz, 1150MW, 4-poles large turbine generator is investigated. The magnetic field and loss at no-load condition of the generator end region are calculated and the calculation results are compared with the test data. The result shows that the calculation model is accurate.

3-D Finite Element Method Analysis of Additional Load Losses in the End Region of Permanent-Magnet Generators

Machine design typically concentrates on the main magnetic and electric circuits while various additional losses are evaluated only by simple empirical equations. The objective of this paper is to examine the importance of the additional losses in the stator end region and in the housing of a 3.1 MW permanent-magnet wind generator. Stator stack clamping ring and finger plate losses are investigated using a 3-D finite element method. 2-D FEM analysis of the stator supporting housing losses is also performed. Two common mechanical component materials are analyzed in the 3-D studies; construction steel and stainless steel. The results show that failure to consider stator end areas and stator supporting constructions at the design stage can result in unwanted additional losses and affect machine efficiency. Indirect verification of the results is provided by efficiency measurements of different versions of the real 3.1 MW machine.

Magnetic field analysis of stator core end region of large turbogenerators

In order to estimate the losses and temperature rise at the end of electrical machines, it is important to clarify electromagnetic behavior in the core end region. In this paper, the method of evaluating the leakage flux of the stator end region of large turbogenerators, combining three-dimensional magnetic field analysis and phasor diagram analysis of the end leakage flux is described. Moreover, the result of applying this method to a 60 Hz-1000 MW turbogenerator is also described.

Under excitation limiter and its role in preventing excessive synchronous generator stator end-core heating

The process of synchronous generator stator end-region (SER) heating in the under-excited condition is investigated using a thermal model based on flux densities consideration. The parameter of the model are identified using the least-square method and from which the SER steady-state and transient thermal responses are determined. A new SER heating limit is derived and used for the design of the under-excitation limiter. The proposed method makes more effective use of the generator capability to absorb reactive power without causing instability, SER overheating, and serious system overvoltage problems.

A Method to Calculate Turbogenerator End Region Fields and Losses and Validation using Measured Results

Modern turbogenerators are designed with high specific loadings. One of the consequences of this is the requirement to design the machine to minimise the size and effects of stator end region leakage fields. This paper describes a finite element method, including both iron saturation and eddy current reaction, to calculate the losses induced in the stator by these fields. The calculations compare favourably with loss densities measured within the stator core of a full size machine. Axial flux densities calculated by the method also show good agreement with flux densities measured on open and short circuit and at full load leading power factor whilst the machine was in service.

Computation and validation against measurements of stator end-region fields in synchronous generators

Computation and validation against measurements of stator end-region fields in synchronous generators

The Influence of Power Factor on Turbogenerator Core End Losses — A Simple Physical Explanation

The object of this paper is to provide a physical explanation for the variations of stator end region magnetic leakage field, and consequent temperature rises, in a turbogenerator. In particular the paper shows how the losses and temperature rises vary with the power factor and load angle of the turbogenerator.